This invention relates to a tape transport for use with transducer means to transport tape along a predetermined path extending past said transducer means, comprising two capstans, each disposed at a respective end of said predetermined path; two rollers, each disposed adjacent a respective one of the capstans and arranged to guide tape beyond the respective end of the path in partial wrapping engagement about its respective capstan; two drive means each coupled to a respective one of said capstans; and control means coupled to the drive means and arranged to control operation thereof to drive said capstans at differing torques whereby to induce a controlled tension in tape extending along said path.
Such tape transports are used with electro-magnetic transducers to transport magnetic recording tape along a predetermined path extending past the transducer, during recording and replay of signals on the tape. In order to provide high fidelity of signal reproduction, which requires an accurate control of tape tension, various techniques are commonly employed. Thus, movement of the tape past the transducers is generally effected, either directly or indirectly, by one or two capstans, driven by an electric motor.
Systems are known, in which two capstans are driven by respective motors to control tape tension, these motors being both driven by respective signals derived directly from an independent source.
For instance, U.S. Pat. No. 3,861,573 (Kawasaki & al.) describes a system with two reference signal generators which supply separate reference signals to a multiplexed differential amplifier for comparison with respective speed signals from tachometers.
In various other systems, such as described in the U.S. Pat. Nos. 3,903,544; 3,930,268; 3,869,723 and 4,122,504, only one drive motor is provided, and either various methods, for example differently-sized pulleys (U.S. Pat. No. 3,583,618) or different contact pressures (U.S. Pat. No. 3,390,268) are used to control tension, or else the capstans are driven in unison (U.S. Pat. Nos. 3,869,723 and 4,122,504). In U.S. Pat. No. 4,097,005 (Sleger), only one capstan is in fact driven.
Such systems still have the problem of certain inaccuracy of the control of tape tension, of vibration in the movement of the tape and of distortion of the produced signal such as wow and flutter, specially under severe conditions such as accelerations or large temperature variations.